Aprilaire
No Power to Humidifier Control Circuit
Aprilaire humidifier does not turn on at all (no click, no water, no fan)
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Blown 24 VAC transformer, Open furnace fuse, Loose R/C connections, Broken low-voltage wire to humidifier, Faulty humidistat
How to Fix / Troubleshooting
Safety first: Turn off furnace power and be cautious when measuring live voltages.
- Check furnace fuse: Inspect the low-voltage fuse on the furnace control board. Replace with the same rating if blown and investigate for shorts.
- Measure transformer output: With power on, measure between R and C at the furnace board or humidifier transformer. You should see 24–28 VAC. If 0 V, the transformer may be failed and should be replaced.
- Verify wiring to humidistat: Confirm the wires from R and C reach the Aprilaire humidistat/control and are firmly connected.
- Bypass humidistat for test: Temporarily jumper the humidifier control terminals (e.g., H to H or HUM to C depending on model) to see if the humidifier energizes. If it does, the humidistat is likely faulty and should be replaced.
- Replace failed component: Install a new Aprilaire 24 VAC transformer or Aprilaire humidistat/control as indicated by testing.
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Repair Difficulty
Hard
4/5
Required Part
Aprilaire 24 VAC Transformer
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